Try 'em both. Never used Oxypowder . Been using colonix for a couple of years. Never any side effects. Either way you need to drink your water. That's key, in either case.
I am big these days on SWF. I fast for a day (water or juices only), do a laxative tea before bed (smoothe move chocolate), let the smoothe move do its thing the next day, drink a lot of water, do a SWF. Works wonders.